Measuring mechanical properties of micro or nano-structural samples is of importance as more modern devices utilize materials and structures at these scales. Micron and nano-mechanical characterization is used to measure and evaluate numerous mechanical properties of materials, including modulus, hardness, fracture toughness, wear resistance and friction coefficients. Nanoindentation has proven to be a method to reveal mechanical properties and sample behavior at scales of microns or less (e.g., micron and nano-scales). Nanoindentation quantitatively measures mechanical properties, such as elastic modulus and hardness, of materials at these scales. In nanoindentation, a nanoindenter capable of determining the loading force and displacement is used.
One variable in predicting material behavior is the evaluation of structures and their material properties while the structures are heated. Hot hardness testing has been used at macro and micron scales previously with some drawbacks, as discussed herein. One of the major problems in testing at elevated temperature is the thermal drift and long term thermal stability of the system. A major source of thermal drift is fluctuations in the temperature of the load frame over time.
In some examples, heating stages are built so the sample material is heated using a macro scale resistive heating stage with very large surface area compared to the test probe dimensions. The tip of the mechanical testing instrument is brought in contact with the specimen surface with a contact force and the probe is allowed to heat passively through the sample. When the probe and the sample system reach a steady state, the thermal drift reaches a steady state and the indentation testing (or other deformation based testing) is carried out. A major problem with this approach is the significant amount of time needed to reach the steady state temperature between each testing procedure. Although thermal drift reaches a steady state where measurements can be done in a few seconds, the drift rates are much higher, making the measurements very unreliable for longer time indents (e.g., around ten seconds or longer). Additionally, the entire volume of the instrument chamber is heated (including the instrument, instrument housing, stage assembly and the surrounding chamber walls encompassing these components).
In other examples atomic force microscopes utilize a cantilever with a heated tip. In this system the cantilever deflection is measured as the tip temperature is increased. The deflection is then used to identify the melting transition. This is a qualitative approach and may only provide a relative estimate of the cantilever penetration for different regions, but does not give any quantitative information.
Another issue with high temperature heating of a sample involves oxidation of one or more of the probe tip, the sample or the sample stage. With high temperature heating, for instance above 80 degrees Celsius, the materials of these components may oxidize and accordingly affect the mechanical properties of testing instruments and stage as well as the sample being tested. Oxidation (or other temperature based chemical reactions) frustrate the accurate and reliable measuring of mechanical characteristics of the samples under consideration.